1. Technical Field
The present disclosure relates to a variable voltage control system and method for a hybrid vehicle that can improve fuel efficiency.
2. Related Art
In general, a hybrid electric vehicle (HEV), as shown in FIG. 1, includes an engine, a motor directly connected to the engine as the main driving source of the vehicle, a clutch and a transmission for power transmission, an inverter that drives the engine and the motor etc., a DC/DC converter, and a high-voltage battery. It further includes a hybrid controller, a motor controller, a battery controller, an ECU for engine control, and a TCU for transmission control, which are connected to communicate with each other by CAN communication.
The hybrid controller is a higher-class controller that generally controls all operations in the hybrid vehicle while directly or indirectly communicating with one or more lower-class controllers. For example, it may control the torque, speed, and the amount of power generation torque of the motor while communicating with the motor controller in a predetermined way. It may also perform relay control and detect a fault related to engine start while communicating with the ECU in a predetermined way.
Further, the hybrid controller may detect the temperature, voltage, current, and SOC (State of Charge) of the battery, control the torque and speed of the motor in accordance with the SOC while communicating with the battery controller, and maintain the velocity desired by a driver while communicating the TCU.
Further, the hybrid controller may control the output voltage of the DC/DC converter to efficiently distribute energy according to the conditions of the vehicle, while monitoring the requirement information (accelerator, brake) of the driver and the present conditions of the controllers (MCU, BMS, ECU, TCU) such that the DC/DC converter makes it possible to supply power corresponding to an electric device load of the vehicle and effectively charge a 12V-battery.
The high-voltage battery can provide power to drive the motor and DC/DC converter, and the battery controller may adjust the amount of charge of the high-voltage battery while monitoring the voltage, current, temperature of the high-voltage battery.
In connection with control of the DC/DC converter, the ECU and the TCU may receive the amount of accelerator-down and a brake signal and provide information to the hybrid controller to determine the charge energy of the vehicle.
With the above-described configuration, the fuel efficiency can be increased and the exhaust performance can be improved.
On the other hand, hybrid vehicles are generally equipped with an alternator for charging the battery. A typical alternator in the art function to set and output a reference voltage according to the ambient temperature and RPM so as to maintain a high, constant voltage for preventing discharge of a sub-battery. When voltage drop occurs for a predetermined time period, the alternator controls the reference voltage to be increased by increasing RPM. In addition, it controls RPM or the engine torque to be increased by generating a specific signal corresponding to high electric device load.
In case of hybrid vehicles equipped with such an alternator, errors or failure may be generated in the operation of headlamps or wipers since only a sub-battery deals with the electric device loads at the time of entering an idle stop. Further, efficiency of the alternator may be deteriorated in a high RPM region. Also, the fuel efficiency is adversely affected by the load of the alternator during acceleration. In addition, a battery temperature sensor and a device for monitoring voltage are required for variable voltage control, which requires additional cost.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.